By-pass for incandescent-electric-lamp circuits.



E. & N. R. BOOTH.

BY-PASS FOR INCANDESOENT ELECTRIC LAMP CIRCUITS.

APPLICATIOIY FILED DBG.26,1913.

Patented Jan. 26, 1915.

UNITED STATES PATENT OFFICE.

EDGAR BOOTH AND NORMAN RUSSELL BOOTH, OF HALIFAX, ENGLAND.

BY-PASS FOR INCANDESGENT-ELEOTRIC-LAMP CIRCUITS.

Specification of Letters Patent.

Patented Jan. 26, 1915.

Application filed December 26, 1913. Serial No. 808,796.

' cent electric lamps in series and to provide each lamp with a by-pass which on the failure of the filament of a lamp is brought into operation and the circuit is then completed through theby-pass and the remain- I ing lamps of the series continue in operation. Such a by-pass may consist of two metal pieces separated by a piece of insulating material which will withstand the electro-motive force across the lamp terminals so long as the filament is intact but the insulating efiect of which is destroyed on a rise of electro-motive force due to the failure of a lamp filament. Now a by-pass of this description has hitherto been very uncertain in action particularly on low voltage circuits and the object of this invention is to construct a by-pass which will be reliable in operation on such circuits.

Figure 1 shows a by-pass constructed according to our invention, and Fig. 2 shows the by-pass of our invention in combination with a lamp socket.

Referring to Fig. 1 of the accompanying drawing which illustrates our invention in section M M are two pieces of metal-preferably metal h: ving a low melting point such as lead-which are pressed together but which are prevented from coming into metallic contact by a piece of insulating material P P. This insulating material which may conveniently be a piece of paper is thinly coated on one side with a conducting material C. C. A suitable substance for this purpose is a mixture of finely powdered carbon or blacklead and Water to which is added a small quantity of ordinary thick gum to make the carbon or blacklead adhere to the paper after it has been dried. This mixture may be applied to the surface of the paper with a fine brush or by means of a pneumatic spray. The paper having been thoroughly dried one or more holes H are'then made through it with a sharp pointed instrument such as a pin or needle, the holes being pricked through from the side of the paper which is coated with the conducting material. \Vhen separated by a. piece of insulating material treated as above the two metal pieces M M are prevented from coming into metallic contact but are connected by the thin coating of carbon or blacklead C C formed through the hole or holes H pricked through the insulating material. The resistance of this circuit through the carbon or blacklead on the sides of the hole or holes compared with the resistance of the filament of a low voltage lamp is very high and under normal circumstancesthat is when the lamp filament is intact-the amount of current passing through the by-pass is negligible. On

the failure of a filament however the consequential rise of electro-lnotive force across the metal pieces M M the carbon or blacklead is fused and destroying part of the insulating material P P allows the metal pieces M M to come into contact and fuse together and the circuit is then completed through the by-pass.

In Fig. 1 of the accompanying drawing the thickness of tlfe metal pieces M M, the insulatingmaterial P P and the coating of 'the conducting substances G C is shown greatly enlarged in order to better illustrate the invention.

A convenient method of embodying a bypass of this description in the cap of an incandescent electric lamp .is described in British Patent No. 27862 of 1911.

What we claim and desire to secure by Letters Patent is:

1. A by-pass for incandescent electric lamp circuits, comprising in combination, two pieces of fusible metal, a paper insulation coated on one side with a fusible sub- .stance and having pin-hole apertures there having a plurality of pinhole apertures therethrough, said black lead being adapted to fuse and destroy the paper insulations upon a rise of the electro-motive force of the circuit, thereby allowing the two pieces of fusible metal to come into contact with In testii'nony whereof we. affix our signaeach other and fuse together. tures in presence of two witnesses.

3. An insulating element for a by-pass FDCAR BOOTH consisting of a piece of paper coated on one AN RUSSELL BOOTH side with a mixture of finely divided black lead, water and thick gum, and having a \Vitnesses:

plurality of pinhole punctures therein, sub- AUGUSTUS E. INGRAM, stantially as described. V R. B. NIGHOLLS. 

